The Prometheus-class was one of the most advanced starships fielded by Starfleet in the late 24th century. It was designed with an unprecedented level of automation, and, combined with its advanced tactical systems, was one of the most powerful combat ships in the Alpha Quadrant. The Prometheus was equipped with advanced phaser arrays, quantum torpedoes, regenerative shields, and ablative armor, and its warp engines were designed to outrun even the fastest starship of the Federation fleet. The Prometheus was so highly classified that only four Starfleet officers were trained on how to operate the prototype ship before it came into service.

A unique feature included in the Prometheus design was the multi-vector assault mode, which allowed the ship to split into three semi-independent sections that could each deliver massive force against an enemy target. All three sections were warp-capable. Combined with the extensive automation, the Prometheus could be run by as few as four people.

In addition to standard automation systems, the design also featured holoemitters on every deck, which allowed the ship's Emergency Medical Hologram (Mark II) to access all areas of the ship (most EMHs were confined to sickbay only).

At the close of the Dominion War, Starfleet found its forces spread too thinly across Federation space. In order to help alleviate this situation, they began a massive rebuilding project to fill in the fleet. Some of these vessels were refurbished from the mothball fleet while others were constructed for this very purpose.

Utopia Planetia undertook many of these construction projects, including the construction of the Prometheus-class USS Tethys. Under the direction of Admiral Harrison, construction began in mid 2382 using the latest in Starfleet design and technology. The engineers took into account information that had been learned from Voyager's journey in the Delta Quadrant as well as data that had been exchanged between the allies during the war.

The Tethys incorporated new warp field geometry that allowed her to break many of the current Federation speed records. In addition, the new field design created less of an environmental impact on the surrounding space. Tactical improvements included increased phaser power as well as two additional torpedo launchers fore and aft.

Thanks to an agreement with the Romulans, Starfleet vessels were granted the right to carry cloaking devices. Some vessels were equipped with Klingon cloaking devices while others were procured from the Romulans. In the case of the Tethys, the device had its origins in the Romulan Empire. As a stipulation, the Romulan government required that a Romulan observer be present during any use of the cloaking device.

When command of the Tethys was granted to Commander Iluvar, known for his expertise in the Briar Patch, a number of specific changes were made. The commander insisted that an additional sensor palate be added so as to allow for more scientific exploration, despite the tactical classification of the vessel. In addition, Commander Iluvar requested that the standard bridge module be swapped out for a Sovereign style bridge. This was due to personal feelings regarding the bridge design. He also made the controversial decision to replace the Mark IV EMH with an original Mark I model.

Construction continued on schedule for launch in early 2384. Iluvar took formal command of the vessel only days before launch. With a partial crew aboard, the Tethys headed out to the Oort Cloud to conduct tests of the various ship systems including the Multi-Vector Assault Mode. The testing was successful and the Tethys docked at McKinley Station to await her first orders.

It wasn't long before the Tethys was dispatched to investigate a series of attacks on merchant shipping near the Black Cluster. Upon their arrival, they learned that the mysterious attacker was a rogue Breen warship. In the process, the Tethys beamed aboard 70 isomorphic projections. Just as the crew was about to uncover exactly what was going on, they were recalled to Starbase 165 for reassignment. The isomorphs were stored for later study by Starfleet.

During the mission, the Tethys saw a few unique improvements based on pure necessity. The first was the addition of polarized hull plating similar to that seen on NX Class Warp 5 vessels of the 22nd Century. This was due to the fact that vessels in the Black Cluster cannot operate with shields active and another method of defense was needed. Second was a SONAR based sensor system designed by Lt. Celestial Dancer, the ship's Chief Science Officer. This system allowed the Tethys to locate the Breen Warship that had been plaguing merchant traffic in the area.

Following the battle with the Romulan Warbird Cloaked Dagger, the Tethys was towed to Starbase 386 for repairs and an overhaul, which included the replacement of the damaged Romulan cloak with a new, more reliable Klingon design. In addition, the Tethys received a few upgrades to her warp core, including a new intermix chamber which was designed to increase efficiency. Other additions included a holographic communication system tied in with the shipwide holoprojection system.

In 2385, the USS Tethys participated in the Battle of Altorus, where she and seven other Starfleet vessels engaged vessels of the Elyshan Guard to rescue Ambassador Mordred Ocal. The Elyshan subspace technologies gave them a significant advantage until it was discovered that tri-cobalt torpedoes had an effect on neutralizing their subspace shields, allowing conventional weapons to penetrate them. Ambassador Ocal was successfully retrieved and the group retreated to Starbase 386 for repairs.

The Tethys has just begun her first refit under the careful supervision of Commander Ka'el Fermat.